The present invention relates to an apparatus and a method for measuring the percentage content of one constituent of a two component fluid mixture. The method and apparatus of the present invention have particular utility in measuring the percentage water content in an oil-in-water emulsion in which the continuous phase is water flowing through an oil pipeline.
Oil-in-water emulsions are commonly employed in the transportation of oil. When using these emulsions, it is beneficial to know the percentage water content of the emulsion. A variety of different techniques have been employed to measure the water content.
In one approach, a percentage water measuring circuit is employed which has a capacitance probe for measuring the specific capacitance of the oil-in-water emulsion. The circuit further includes a reference capacitor of known value in series with the capacitance probe, a variable gain alternating-current voltage generator connected in series with the reference capacitor and the capacitance probe for applying an alternating-current voltage across each, a voltage measuring circuit for measuring the actual voltage differential across the probe, an error detecting circuit for detecting the difference between the actual voltage differential across the capacitance probe and a predetermined voltage, a voltage measuring circuit for obtaining the voltage differential appearing across the reference capacitor and a non-linear to linear function generator to convert the voltage differential to a linear function with respect to the percentage water content. A system employing this type of circuit is shown in U.S. Pat. No. 3,768,006 to Mueller.
The primary deficiency of this approach has been the complexity of the circuitry involved. Additionally, questions have been raised as to the accuracy of the measurements.
Other approaches to determining the water content in oil are shown in U.S. Pat. Nos. 4,240,028 to Davis, Jr., 4,289,020 to Paap, 4,429,273 to Mazzagatti and 4,820,970 to Swanson. The Davis, Jr. patent is directed to an apparatus which includes a sensor spacially arranged within a pipe for providing a signal whose frequency and amplitude corresponds to the water saturation. The sensor senses capacitance changes in the oil-in-water emulsion flowing through the pipe. A circuit connected to the sensor provides a signal corresponding to the difference between the sensor signal and a reference signal established for a 100% water saturation. The water content is determined from this difference signal.
The Paap patent relates to a microwave-gamma ray water-in-crude monitor. A microwave transmitter and a gamma ray source are arranged with a measuring cell through which crude oil flows and are used to transmit microwave energy and gamma rays through the cell. A microwave receiver and a gamma ray detector receive the energies transmitted through the measuring cell and provides signals in accordance with the received energies. Apparatus connected to the microwave receiver and to the gamma ray detector provide a display of the water content of the crude oil in accordance with the signals from the microwave receiver and the gamma ray detector.
The Mazzagatti patent relates to an oil-in-water monitor which includes a test cell having a production stream passing through it so as to allow the dielectric properties of the production stream to be monitored. An analyzer connected to the measuring cell provides an indication of the water content of the production stream in accordance with the dielectric properties of the production stream.
The Swanson patent relates to a microwave system for determining the volume fraction of water in a fluid. A microwave beam having a frequency which varies with time is transmitted through the liquid and absorption losses are calculated. The volume fraction of water is determined according to the absorption losses.
These additional techniques have not significantly improved the measurement of the percentage water content of an oil-in-water emulsion.